Looking for a Very Specific Adjective

Question

Is there a word to describe a person who is both of the following?

a) insidious - in the traditional sense...that they have a tendency to use or harm people in such a way that the victim does not realize that harm has begun and may not realize that it's been done until much later.

b) cunning, but licit -- someone for whom the ends justify even the most devious of means but ONLY insofar as the means are aligned with the letter of the law or with otherwise-accepted social norms (irrespective of whether said means are in alignment with the spirit of the law or with the nature and severity of the ends). A sleazy personal injury lawyer, a patent troll, and a professional plaintiff would all be examples of this.

There's a Russian word for this: коварный. Was wondering if there's an English equivalent with matching nuance.

Please note: this is not a request for translation.

Answer 1

Perhaps guileful or Machiavellian.

guileful (from Wiktionary, 2019):

Full of guile; treacherously deceptive.

with guile being (from Wiktionary, 2019):

Astuteness often marked by a certain sense of cunning or artful deception.

---

Machiavellian (from Wiktionary, 2019):

Attempting to achieve goals by cunning, scheming, and unscrupulous methods, especially in politics or in advancing one's career.

Answer 2

"Sly" could be a word for a person who is shady, traitorous, cunning and so on.